1. Field of the Invention
The present invention is directed to a method for the operation of an electrographic printer or copier, whereby a layer containing toner particles, referred to in brief as a toner layer, is deposited on a toner acceptance surface under the influence of a force field.
2. Description of Related Art
Such a method is implemented in the developer unit that is set forth in U.S. Pat. No. 4,777,106. Given this developer unit, the toner particles are electrically charged in a toner reservoir wherein a toner-air mixture is located and the toner particles are subsequently deposited on the toner acceptance surface that is grounded or provided with a potential, being deposited thereon as a toner layer under the influence of an electrical force field. Due to the rotation of a developer drum whose generated surface forms the toner acceptance surface, the deposited toner particles are conducted past a development gap between the developer drum and a toner image carrier. The toner image carrier carries a latent charge image onto which toner particles are selectively applied at the development gap, whereby a toner image arises. The toner image is then applied onto an ultimate image carrier, for example onto paper, from the toner image carrier with or without employment of an intermediate image carrier.
A developer unit having more than one toner acceptance surface is explained in European Patent EP 0 494 454 B 1. The second toner acceptance surface is the generated surface of a transfer drum on which the toner particles are applied directly from the reservoir. The toner particles are then deposited onto the surface of the developer drum at a transfer gap between the transfer drum and the developer drum.
What is disadvantageous about the known method is that a monitoring of the developing process and, in particle, of the amount of toner output by the developer unit is not possible. When the toner amount per surface on the toner acceptance surface or the charge of the toner particles during developing as well lies below or above a predetermined rated value or, respectively, rated range, then the error is not recognized until the finished print image. A reaction thus ensues relatively late. The disturbances in the print image are particularly noticeable given picture elements in the print image that are printed large-area.
In the known method, it is also not possible to exactly set the toner mass per surface section on the toner acceptance surface or the toner charge per surface section, to keep it constant during printing mode and to potentially adapt it to specific print jobs.
U.S. Pat. No. 5,212,522 discloses a method and an apparatus for controlling the mass-related toner charge q/m. The width of a gap between developer drum and a doctor for defining the thickness of the toner layer on the developer drum is employed as a manipulated variable. The gap width is modified with an additional adjustment mechanism. The rotational speed of the toner image carrier and the rotational speed of the developer drum are employed as an auxiliary manipulated variable.
Given a toner concentration monitoring mechanism according to German Patent Document DE 29 30 782 C2, a photo sensor is employed for acquiring the actual toner mass per unit of area on the developer drum. Dependent on the output signal of the photo sensor, the concentration of the toner in a two-component developer is slowly increased.
A developer unit is explained in PCT Patent Application WO, A, 95 10801. The developer unit contains a toner reception surface and an electrode. The toner mass per surface section is acquired with the assistance of a sensor unit. The strength of the charge field between the electrode and the toner reception surface (developer drum) is then set dependent on the output signal of the sensor unit in order to set the toner mass to a rated value.
European Patent Application EP A 0 520 144 explains a developer unit in which the mass relationship between toner and carrier particles is acquired with the assistance of a sensor. Dependent on the acquired mass relationship, printing process parameters such as the charge potential of the photoconductor, the bias potential of the developer unit, the illumination or the toner density are then controlled such an a control procedure that the influence of a modified mass relationship on the quality of the print image is compensated.
The Abstract of Japanese Patent Application JP, A, 0 4 238366 explains a method for the control of the toner concentration in a two-component toner. An optical sensor acquires the toner concentration. A motor for the delivery of toner is then controlled such in a control circuit dependent on the output signal of the sensor that a predetermined toner concentration is established. The optical density of a test mark that is located outside the image region is acquired in a second control circuit with the assistance of a sensor. Parameters of the printing process are then controlled such dependent on the output signal that a predetermined optical density derives.
Both dry toner as well as liquid toner are employed as toner. Given liquid toners, for example, mechanical devices with electrical auxiliary potential are employed for applying the toner. The toners that are employed can still be divided into a single-component and multi-component toner.
What are understood by the term electrographic printer are, in particular, electrophotographic printers, ionographic printers and magnetographic printers. It is also known to employ bands on which the toner layer is deposited instead of the developer drums.